Add simulation and tests for creating multi-environment checks:

- createMix - Create a mixture in X individuals per N 'M-modal' normals
- plot4Nmixture - Plot 4 conditions created by createMix as histograms
- createMix.test - Tests Create mix and the plot4Nmixture function
Merge pull request #43 from DannyArends/master

Add code for simulation and tests to create multienvironment tests